Expandable implants are known in the field of spinal surgery. Many expandable implants require complex mechanisms in order to expand the implant. Greatly simplifying the expansion of an expandable implant is a device taught by Michelson in U.S. patent application Ser. No. 09/551,964, the disclosure of which is incorporated by reference herein, that moves the implant from a collapsed position to an expanded position with less than one full turn of an expander used to expand the implant. Expandable implants often have no provision for preventing the over-expansion of the implant while the implant is being expanded in the disc space. One of the embodiments of expandable implants taught by Michelson in the '964 application utilizes a hook and peg arrangement that is integral with the implant to prevent over-expansion.
In certain circumstances, the upper and lower members of the expandable implant can move away from one another and merely securing the upper and lower members to the adjacent vertebral bodies either with vertebral body engaging projections or with bone screws is not adequate. An example of such a circumstance occurs when the surgeon elects to approach the spine anteriorly, which generally requires severing and/or removing substantial portions of the anterior longitudinal ligament over the operated area. The anterior longitudinal ligament is positioned along the anterior spinal surface and prevents hyperextension of the spine as an individual bends backward. Because the anterior longitudinal ligament covers the anterior spinal surface, the surgeon must cut through this tough ligament to access the disc space below, compromising the stability of the spine. Specifically, the anterior longitudinal ligament is generally lax, except when an individual leans backward, then the ligament acts as a tension band resisting elongation. If the anterior longitudinal ligament is damaged, there is no check on that spinal movement and the vertebral bodies may detrimentally angulate. Thus, what is needed is a simple, easy-to-use device that can either or both expand and prevent the over-expansion of an implant, and further can be used, if desired, to lock bone screws to an implant having bone screws therein.